1. Field of the Invention
The present invention relates to a printer to which power is supplied by a switch mode power supply (SMPS), and more particularly, to an apparatus for and a method of controlling a supply of power to a printer, to save power consumption by automatically turning on the power supply in accordance with a predetermined print command, and automatically turning off, or reducing the supply of power to the printer when there is no printing operation for a predetermined time period.
2. Description of the Related Art
A general printer prints image data originating in the printer, or external image data received from a connected host such as a computer on a paper with a medium such as ink or toner. Since the printer is operated only when a printing job is assigned, the printer does not always need electrical power for operation. However, as long as the printer is turned on, the printer is supplied with power even when the printer is not in the printing operation.
Generally, a switch mode power supply (SMPS) has been used for supplying power to the printer. A SMPS supplies power as required by the load of the printer. FIG. 1 shows a circuit diagram of a conventional SMPS, for supplying power to, for example, a control unit (or microcomputer) of the printer and peripheral devices of the printer.
Referring to FIG. 1, in the conventional SMPS, as the alternating current switch SW1 is turned on, an AC voltage is transformed into a DC voltage at a first rectifier circuit 101 so that the DC voltage is transmitted to a driving voltage supply unit 105 and a primary winding Np of a transformer. Initially, the driving voltage is not supplied to a pulse width modulation-IC (PWM-IC) 110 and accordingly, power is not switched in the primary winding Np. The driving voltage supply unit 105 comprises start-up resistors R1 and R2, a capacitor C1, a resistor R3 and a diode D1, and supplies a driving voltage Vcc to the PWM-IC 110. The capacitor C1 is charged with DC voltage from the first rectifier circuit 101 through the start-up resistors R1 and R2. As the voltage is charged to the capacitor C1, a driving voltage Vcc is supplied to the PWM-IC 110 through a terminal P1 of the PWM-IC 110. Accordingly, the PWM-IC 110 outputs, through a terminal P3, a control signal that controls switching of a field effect transistor FET which has a source and a drain serially connected with the primary winding Np. The control signal is applied to a GATE terminal of the FET through a resistor R4. As the FET is turned on, the primary winding Np of the primary side in a transformer 115 causes the power to be induced at secondary windings Ns1 and Ns2 of a secondary side of the transformer 115, and at an auxiliary winding Na.
As the power is induced at the auxiliary winding Na of the transformer 115, the PWM-IC 110 is supplied with driving voltage through the diode D1 and the resistor R3 of the driving voltage supply unit 105. If the FET is turned off and thus there is no power induced at the secondary winding Na, the PWM-IC 110 is supplied with the driving power from the electric current charged in the capacitor C1.
As described above, power induced at the secondary windings Ns1, Ns2, Na is determined in accordance with the switching of the FET. The FET switches in accordance with a duty cycle that is determined at the PWM-IC 110 based on a signal provided from a feedback unit 120 through a terminal P4 of the PWM-IC 110. The feedback unit 120 detects voltage Vo1 output to a control unit 130, and accordingly provides the terminal P4 of the PWM-IC 110 with the feedback signal to maintain the output voltage Vo1 at a constant value. The PWM-IC 110 measures a voltage across a resistor R5 which corresponds to a peak of a current which flows through the FET through a terminal P2 of the PWM-IC 110, and prevents an overcurrent from flowing through the FET. More specifically, upon sensing the overcurrent at the FET, the PWM-IC 110 controls the FET to stop switching and to remain in an off state.
Meanwhile, AC power, which is induced at the secondary windings Ns1 and Ns2, is rectified and smoothed into DC voltages V02 and V01, respectively. The DC voltage V02 is supplied by a diode D2 and capacitors C2 and C3 and supplies peripheral devices 125 and the DC voltage V01 is supplied by a diode D3 and capacitos C4 and C5 and supplies the control unit 130.
If the AC switch SW1 is turned off, the SMPS shown in FIG. 1 stops supplying power to the peripheral devices 125 and the control unit 130.
Accordingly, unless the AC switch SW1 is turned off, the conventional SMPS supplies the power to the control unit 130 and the peripheral devices 125. Thus, to save power, a user is required to turn off an AC switch of a corresponding system that is not in use. However, the user usually turns off the printer by manipulating on the power key on the printer panel, only cutting off power to some peripheral devices of the printer, but continuing to supply power to other peripheral devices. As a result, power is consumed unnecessarily.
A sleep mode has been suggested, in which, when the printer is determined not to have been operated for a predetermined time period, the power supply from the SMPS to all the peripheral devices is stopped, but the control unit continues to be supplied with power. The SMPS keeps supplying power to the control unit, and continues to make power available to the peripheral devices.
Since the conventional printer requires design specifications that enable the printer to be turned on all day, design cost for a power supplying device increases. Further, many users who turn off a computer having a connected printer after use leave the connected printer turned on. Accordingly, power is wasted.
The AC switch SW1 installed on the power supply line must have a sufficiently high rating to withstand utility AC voltages such as 110V or 220V. Accordingly, the price of the AC switch is high.
Finally, the AC switch SW1 is required to have a current capacity to withstand an inrush current that is incurred by smoothing capacitor (not shown) in the rectifier circuit every time the AC switch SW1 is turned on.